(a) Field of the Invention
The present invention relates to a charge pump, a DC-DC converter, and a method thereof. More particularly, the present invention relates to a high efficiency charge pump, a DC-DC converter including the charge pump, and a method of improving power efficiency of the DC-DC converter.
(b) Description of the Related Art
A digital circuit within a driving chip of a flat panel display is a low voltage circuit that operates with a voltage of about 3V, which is a supply voltage of a chip. However, an analog output stage of a scan driving circuit and a data driving circuit for driving a panel of an organic light emitting device (“OLED”) is composed of a high voltage circuit. A voltage of about 10 to 20V is applied, depending on characteristics of the display panel. Therefore, a DC-DC converter, which receives a supply source voltage of about 3V and generates a high voltage required for output stages of the data driving circuit and the scan driving circuit, is required. Specifically, the DC-DC converter requires low-power and high efficiency of design technology because it is used in a portable instrument.
The DC-DC converter may be divided into a switching type and a charge pump type. A charge pump type of DC-DC converter having high power efficiency is generally used in a display device for a portable instrument.
However, when the charge pump type is used, a voltage drop is generated due to a threshold voltage of charge transfer transistors constituting the charge pump. Accordingly, in a structure in which power consumption is generated and a high voltage and a high current are output, there is a problem that power loss is further increased and thus efficiency is reduced.